02-09-2013, 03:56 PM
Friction stir welding(FSW)
Friction stir .docx (Size: 1.08 MB / Downloads: 86)
ABSTRACT:-
Friction stir welding(FSW), a new solid state joining process combining deformation heating and mechanical work to obtain high quality, defect-free joints. Friction stir welding is well suited for joining aluminium alloys in a large range of plate thickness and has particular advantage over fusion welding when joining of highly alloyed aluminium is considered, high quality joints may even be made in discontinuously reinforced aluminium alloys. Because of the many demonstrated advantage of FSW over fusion welding techniques, the commercialization of friction stir welding is proceeding at a rapid pace. Current production application includes both large and small scale products.
INTRODUCTION
In many industrial applications steels are readily replaced by nonferrous alloys, in most cases by aluminum alloys. Some of these materials combine mechanical strength comparable with structural steels and low weight, allowing for a significant reduction of weight. While production of components of aluminum alloys is not very complex, joining of these materials can sometimes cause serious problems. Lack of structural transformations in solid state and excellent thermal and electrical conductivity cause problems in fusion and resistance welding of aluminum alloys. That led to the development of Friction Stir Welding a solid state joining technique in which the joined material is plasticized by heat generated by friction between the surface of the plates and the contact surface of a special tool, composed of two main parts: shoulder and pin. Shoulder is responsible for the generation of heat and for containing the plasticized material in the weld zone, while pin mixes the material of the components to be welded,thus creating a joint. This allows for producing defect-free welds characterized by good mechanical properties.
WORKING PRINCIPLE
Traditionally, friction welding is carried out by moving one component relative to the other along a common interface, while applying a compressive force across the joint. The friction heating generated at the interface softens both components, and when they
become plasticized the interface material is extruded out of the edges of the joint so that clean material from each component is left along the original interface. The relative motion is then stopped, and a higher final compressive force may be applied before the joint is allowed to cool. The key to friction welding is that no molten material is generated, the weld being formed in the solid state
FSW of aluminium
The most popular aluminum alloy contains about 8 wt% of silicon.
_ It therefore solidifies to primary aluminum-rich dendrites and a eutectic mixture of aluminum solid-solution and almost pure silicon.
_ The latter occurs as coarse silicon particles which tend to be brittle.
_ The cast alloy usually has some porosity.
_ Friction stir welding has the advantage that it breaks up the coarse silicon particles and heals any pores by the mechanical processing, as illustrated below.
PARAMETERS
1. Flow of material
Material motion occurs by two processes:
Material on the advancing front side of a weld enters into a zone that rotates and advances with the pin. This material was very highly deformed and sloughs off behind the pin to form arc-shaped features when viewed from above (i.e. down the tool axis). It was noted that the copper entered the rotational zone around the pin, where it was broken up into fragments. These fragments were only found in the arc shaped features of material behind the tool. The lighter material came from the retreating front side of the pin and was dragged around to the rear of the tool and filled in the gaps between the arcs of advancing side material. This material did not rotate around the pin and the lower level of deformation resulted in a larger grain size.
2.Generation and flow of heat
For any welding process it is, in general, desirable to increase the travel speed and minimize the heat input as this will increase productivity and possibly reduce the impact of welding on the mechanical properties of the weld. At the same time it is necessary to
ensure that the temperature around the tool is sufficiently high to permit adequate material flow and prevent flaws or tool fracture.
ADVANTAGES AND DISADVANTAGES
A number of potential advantages of FSW over conventional fusion-welding processes have been identified.
Good mechanical properties in the as welded condition.
Improved safety due to the absence of toxic fumes or the spatter of molten material.
No consumables - conventional steel tools can weld over 1000m of aluminium and no filler or gas shield is required for aluminium.
Easily automated on simple milling machines - lower setup costs and less training.
Can operate in all positions (horizontal, vertical, etc), as there is no weld pool.
Generally good weld appearance and minimal thickness under/over-matching, thus reducing the need for expensive machining after welding.
Low environmental impact.
CONCLUSION AND FUTURE SCOPE
FSW is the best process to welding Aluminum for long lengths with an excellent quality. Considerable effort is being made to weld higher temperature materials such as titanium and steels by using FSW. Take the process beyond its current use of mainly simple butt and lap joint configurations and make it a much more flexible fabrication
process.
Friction stir .docx (Size: 1.08 MB / Downloads: 86)
ABSTRACT:-
Friction stir welding(FSW), a new solid state joining process combining deformation heating and mechanical work to obtain high quality, defect-free joints. Friction stir welding is well suited for joining aluminium alloys in a large range of plate thickness and has particular advantage over fusion welding when joining of highly alloyed aluminium is considered, high quality joints may even be made in discontinuously reinforced aluminium alloys. Because of the many demonstrated advantage of FSW over fusion welding techniques, the commercialization of friction stir welding is proceeding at a rapid pace. Current production application includes both large and small scale products.
INTRODUCTION
In many industrial applications steels are readily replaced by nonferrous alloys, in most cases by aluminum alloys. Some of these materials combine mechanical strength comparable with structural steels and low weight, allowing for a significant reduction of weight. While production of components of aluminum alloys is not very complex, joining of these materials can sometimes cause serious problems. Lack of structural transformations in solid state and excellent thermal and electrical conductivity cause problems in fusion and resistance welding of aluminum alloys. That led to the development of Friction Stir Welding a solid state joining technique in which the joined material is plasticized by heat generated by friction between the surface of the plates and the contact surface of a special tool, composed of two main parts: shoulder and pin. Shoulder is responsible for the generation of heat and for containing the plasticized material in the weld zone, while pin mixes the material of the components to be welded,thus creating a joint. This allows for producing defect-free welds characterized by good mechanical properties.
WORKING PRINCIPLE
Traditionally, friction welding is carried out by moving one component relative to the other along a common interface, while applying a compressive force across the joint. The friction heating generated at the interface softens both components, and when they
become plasticized the interface material is extruded out of the edges of the joint so that clean material from each component is left along the original interface. The relative motion is then stopped, and a higher final compressive force may be applied before the joint is allowed to cool. The key to friction welding is that no molten material is generated, the weld being formed in the solid state
FSW of aluminium
The most popular aluminum alloy contains about 8 wt% of silicon.
_ It therefore solidifies to primary aluminum-rich dendrites and a eutectic mixture of aluminum solid-solution and almost pure silicon.
_ The latter occurs as coarse silicon particles which tend to be brittle.
_ The cast alloy usually has some porosity.
_ Friction stir welding has the advantage that it breaks up the coarse silicon particles and heals any pores by the mechanical processing, as illustrated below.
PARAMETERS
1. Flow of material
Material motion occurs by two processes:
Material on the advancing front side of a weld enters into a zone that rotates and advances with the pin. This material was very highly deformed and sloughs off behind the pin to form arc-shaped features when viewed from above (i.e. down the tool axis). It was noted that the copper entered the rotational zone around the pin, where it was broken up into fragments. These fragments were only found in the arc shaped features of material behind the tool. The lighter material came from the retreating front side of the pin and was dragged around to the rear of the tool and filled in the gaps between the arcs of advancing side material. This material did not rotate around the pin and the lower level of deformation resulted in a larger grain size.
2.Generation and flow of heat
For any welding process it is, in general, desirable to increase the travel speed and minimize the heat input as this will increase productivity and possibly reduce the impact of welding on the mechanical properties of the weld. At the same time it is necessary to
ensure that the temperature around the tool is sufficiently high to permit adequate material flow and prevent flaws or tool fracture.
ADVANTAGES AND DISADVANTAGES
A number of potential advantages of FSW over conventional fusion-welding processes have been identified.
Good mechanical properties in the as welded condition.
Improved safety due to the absence of toxic fumes or the spatter of molten material.
No consumables - conventional steel tools can weld over 1000m of aluminium and no filler or gas shield is required for aluminium.
Easily automated on simple milling machines - lower setup costs and less training.
Can operate in all positions (horizontal, vertical, etc), as there is no weld pool.
Generally good weld appearance and minimal thickness under/over-matching, thus reducing the need for expensive machining after welding.
Low environmental impact.
CONCLUSION AND FUTURE SCOPE
FSW is the best process to welding Aluminum for long lengths with an excellent quality. Considerable effort is being made to weld higher temperature materials such as titanium and steels by using FSW. Take the process beyond its current use of mainly simple butt and lap joint configurations and make it a much more flexible fabrication
process.